• Research progress of biomass catalytic pyrolysis for bio-oil production and bio-oil modification for quality improvement

    ZHAO Rongyang;YANG Meiling;LI Jie;CHANG Guozhang;WANG Cuiping;Clean Energy Laboratory,College of Civil Engineering and Architecture,Shandong University of Science and Technology;

    Based on the national carbon neutral background, the effective use of biomass, as an important renewable resource, is crucial. Pyrolysis of biomass for oil production has the potential to achieve large-scale production, which has become the main content of biomass utilization. Biomass pyrolysis technology can be divided into direct liquefaction and indirect liquefaction according to different liquefaction methods.The components of bio-oil obtained from direct biomass liquefaction is unstable, and the quality of the bio-oil obtained from indirect liquefaction depends on the reactor type, reaction temperature, and catalyst type. The quality of bio-oil varies greatly due to different preparation methods, and it′s necessary to modificate and upgrade the bio-oil for its practical application. The types of catalysts used to improve the quality of bio-oil during biomass pyrolysis were summarized and compared. The technical routes for the modification and upgrading of raw bio-oil after separation into light and heavy components were emphatically reviewed, which could transform into gas or fuel oil or even chemicals to realize the high-value application of the bio-oil. The modification methods for light oil components include production hydrogen by steam reforming, catalytic cracking, hydrodeoxygenation, catalytic esterification, and other processes. The type of catalyst is mainly molecular sieve and precious metals. However, the heavy oil component has low water content, high viscosity, and there are few related upgrading studies. At present, hydrogenation, catalytic cracking, catalytic esterification, solvent addition, and gasification are mainly reported. Catalyst, hydrogen source, and energy consumption are the main reasons for limiting their scale and industrial application of bio-oil upgrading and modification methods. Reducing the cost of the catalyst and improving the catalyst life, reducing the use of hydrogen source or using low cost hydrogen source, simplifying the process, and decreasing reaction temperture are the development direction of bio-oil upgrading technology.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 12595K]

  • Preparation and application of coal-based functional carbon materials

    FENG Shizhan;LENG Changyu;WANG Luxiang;GONG Xinyi;XU Menjiao;GUO Nannan;AI Lili;ZHANG Qing;School of Chemistry,Xinjiang University;

    Based on the technology theories of molecular chemical engineering and nanomaterials science, the development and application of coal-based functional carbon materials are of great significance to realize the clean utilization of coal resources, as well as the upgrading of high-value-added coal industries. Coal is the natural materials consisting of aromatic and hydrogenated aromatic groups with a three-dimensional(3D) cross-linked network structure. The unique molecular properties of coal(coal derivatives) provide great potential for the synthesis of a variety of coal-based functional carbon materials. Much progress has been made in coal-based functional carbon materials in the last two decades, which needs to be clarify the current status and development direction of functional carbon materials prepared from coal and its derivatives. The controlled preparation of zero-dimensional to three-dimensional coal-based functional carbon materials has been achieved by using molecular shear, chemical vapor deposition, arc discharge, electrostatic spinning, and other technical means, and the current research status of coal-based graphene carbon quantum dots, carbon spheres, carbon nanotubes, carbon fibers, coal-based graphene and coal-based porous carbon has been systematically sorted out. The advantages and shortcomings of multi-dimensional coal-based functional carbon materials in the fields of energy storage, catalysis, and interfacial separation were summarized. It analyzed and discussed the problems faced by coal-based functional carbon materials such as low controllability, complex molecular structure and the difficulty of synthesis means for large-scale application. This review will provide some reference and insight into the design, preparation, and application of novel coal-based functional carbon materials.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 138613K]

  • New research progress on needle coke: From raw materials to preparation methods

    ZHENG Xiankang;QIN Zhihong;YANG Xiaoqin;LIN Zhe;School of Chemical Engineering and Technology,China University of Mining and Technology;

    Needle coke, as a high value-added product in the coal and petroleum industries, is an essential raw material for producing ultra-high-power graphite electrodes, and its domestic demand is increasing. Due to the lack of in-depth understanding of the production process of needle coke, high-quality needle coke has not yet been produced on a large scale in China. In recent years, more and more researchers have turned their attention to modifying raw materials through various methods to expand the selection range of raw materials and improve their properties, thereby producing high-quality needle coke. In this paper, the effects of different component and structure in raw materials on the preparation of needle coke were reviewed, and the requirements of composition and properties for raw materials were summarized. Good raw materials should have low quinoline-insoluble, low impurity atom content, and high aromatic content, while also having moderate reactivity. The pretreatment can effectively improve the composition of raw materials and remove the components which are harmful to the formation of mesophase. By comparison, the combination of multiple pretreatment methods can get better effect than single pretreatment method, pre-heating can reduce the impact of small molecular compounds on subsequent reactions. Co-carbonization method is the most commonly used preparation method. Among the three co-carbonization agents, the nucleation-induced agents can play a nucleus role in the formation of mesophase spheres and promote the formation of mesophase, but may introduce impurities that cannot be assimilated. Polycondensation catalysts can greatly shorten the reaction time, but are not conducive to controlling the reaction in a stable and difficult to be removed from the product. Raw material modifiers can improve the performance of needle coke products and reduce the cost by optimizing the composition of raw materials, which has the best application prospect in industrial production. Coal dense medium component(DMC) separated by extraction and back-extraction method is the origin substance to form mesophase in coking coals. As a new high-quality raw material for needle coke producing, DMC has many advantages such as low ash content, low quinoline insoluble content, high hydrogen carbon ratio, and not require further pretreatment process. The mesophase and needle coke prepared from DMC have excellent performances.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 33020K]

  • Research progress in preparation of lignite based activated carbon

    DONG Zilong;WU Zhenshen;LI Mengke;HUANG Yajie;CHEN Junmin;LI Lixin;YANG Qiaowen;LIU Yunfu;WU Jie;XIE Liping;School of Environment and Chemical Engineering,Heilongjiang University of Science and Technology;School of Chemistry and Environmental Engineering,China University of Mining and Technology-Beijing;

    Lignite has rich resources, low price, many pores, rich functional groups, mainly phenolic hydroxyl, high reaction activity, short activation time and other characteristics. Based on the advantages of lignite properties, the preparation of activated carbon from lignite has attracted much attention. Lignite based activated carbon is widely used in industrial gas purification, wastewater treatment, coal based electrode and supercapacitor. As lignite has low calorific value and high pollutant emission, it is of great significance to prepare high value-added activated carbon from lignite. The pore structure, specific surface area and pore size distribution of activated carbon restrict the development of lignite based activated carbon. In order to enhance the adsorption capacity of activated carbon, different preparation methods were used to adjust the pore structure. The properties of lignite and the main factors affecting the properties of lignite based activated carbon, including raw materials, coal blending and lignite briquetting conditions, are reviewed. The preparation methods of activated carbon from lignite include chemical method(hydrochloric acid, phosphoric acid, potassium hydroxide), physical method(steam, carbon dioxide and flue gas) and physical chemical method(chemical gas combined activation and microwave assisted chemical activation). The mechanism of different preparation methods of lignite activated carbon was described. The problems in preparation of activated carbon from lignite were prospected.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 20712K]

  • Modulation and catalytic application of coal-based carbon dots and its composite

    CAI Tingting;HU Shengliang;School of Energy and Power Engineering,North University of China;Department of Chemistry and Chemical Engineering,Lyuliang Univergity;

    Preparation of novel coal-based carbon materials from coal and its derivatives complies with the Carbon peaking and carbon neutrality goals, which is also an effective strategy to enhance the standards of coal-based fine chemicals and improve the economic benefits of the coal industry. In recent years, the research on the preparation and application of coal-based carbon dots(CDs) has been clearly demonstrated and their role in regulating the compound formation and energy conversion has also been discovered. In this paper, the synthesis and control strategy of coal-based CDs were reviewed firstly. Secondly, the functions of CDs in compound synthesis were emphasized, including the inducing of heterogeneous nucleation, reduction and stabilization, and self-assembly as the load carrier. Furthermore, the application progress in catalysis was summarized from the following aspects of photocatalytic organic degradation and chemical synthesis, electrocatalysis and nanozyme. This paper aims to summarize the research achievements and remaining problems in the field of coal-based CDs, thus to promote the design and development of various new coal-based materials and achieve efficient and highly selective catalytic reactions.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 17621K]

  • Structural and pyrolysis characteristics of two high-temperature pitches

    ZHOU Xingmiao;YANG Tao;SONG Yan;LIU Zhanjun;Key Laboratory of Carbon Materials,Institute of Coal Chemistry,Chinese Academy of Science;Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Science;

    Shenhua coal liquefaction pitch(CLP, softening point: 403.15 K) and Yongdong coal tar pitch(CTP, softening point: 383.65 K) were analyzed using group composition analysis, elemental analysis, FT-IR, NMR and GPC. The average molecular structure model of the soluble were obtained. The pyrolysis characteristics of CLP and CTP were analyzed by TG, and the kinetics were calculated by Coats-Redfern and DAEM models, respectively. The results show that the CLP has lower aromatization and condensation degree compared with the CTP. The pyrolysis of the two pitches can be divided into three stages with the main process ranges from 473.15-873.15 K. CLP has concentrated pyrolysis process due to the narrow molecular weight distribution and small degree of condensation of molecular structure. The pyrolysis product release index R_H of CLP is larger. The average activation energy calculated by the Coats-Redfern method is 35.03 kJ/mol for CLP and 37.98 kJ/mol for CTP. In the DAEM model, with the increase of conversion α, the E of the two pitches increase. The E increases significantly especially when α> 0.5. According to the fitting correlation coefficient R~2 of the two kinetic models, the C-R model and DAEM model are suitable for the pyrolysis process of CTP.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 32723K]

  • Fabrication of modified pitch-based hard carbon materials for high-performance sodium-ion storage

    CHEN Tao;WU Jihao;CHE Xiaogang;LIU Siyu;HAN Xinghua;ZHENG Yiting;YANG Juan;School of Chemistry and Chemical Engineering,North University of China;School of Chemical Engineering and Technology,Xi′an Jiaotong University;

    The controllable fabrication and structural optimization of carbon anode materials for sodium-ion batteries(SIBs) are one of the leading research directions in the field of electrochemical energy storage. Herein, the coal tar pitch from industrial byproduct was first used as the carbonous precursors to surface modification by a chemical cross-linking reaction of 1,4-benzenedimethanol, and then the hard carbon materials for SIBs were successfully prepared through high-temperature carbonization treatment.Combined with a series of characterization technologies including SEM, TEM, and nitrogen(N_2) adsorption/desorption tests, it is confirmed that the chemical cross-linking modification of coal tar pitch could significantly restrain the graphitization degree of carbon materials, and thereby further increase layer spacing(0.373 nm) and carbon layer disorder. Meanwhile, the particle size of the obtained hard carbon material is minimized from 15 μm to about 2 μm. The electrochemical measurements demonstrate that the modified pitch-based hard carbon material(HC-1300) shows a high initial Coulombic efficiency of 80.1% and a specific capacity of 232.2 mAh/g at 0.1 A/g, which is significantly superior to that of the sample(DC-1300) obtained by direct carbonization.In addition, the HC-1300 sample delivers a specific capacity of 171.1 mAh/g at a high current density of 5 A/g and excellent capacity retention of 74.9% after 1 500 charging/discharging cycles, suggesting excellent rate performance and cycling stability.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 27208K]

  • Preparation of high oxygen content lignite based porous carbon spheres for supercapacitor by one-step KHCO_3 activation

    YANG Zhihui;CAO Jingpei;ZHUANG Qiqi;WU Yan;ZHAO Xiaoyan;Jiangsu Province Engineering Research Center of Fine Utilization of Carbon Resources (Ministry of Education),China University of Mining & Technology;

    As an organic macromolecule rich in oxygen-containing functional groups, lignite is considered as a natural precursor for the preparation of oxygen-enriched porous carbon. Lignite modified by acid washing followed with oxidization(OAWSL) was obtained for increasing the oxygen content. With the activation of KHCO_3, a large number of bubbles penetrate the carbon layer and escape to form abundant pores at high temperature, and a unique spherical surface is obtained. What′s more, the effect of the addition of KHCO_3 on the structure and the electrochemical performance of porous carbon as electrode material for supercapacitors was investigated. It is found that the porous carbon spheres, which is prepared under the condition of the mass ratio of 1∶3(OAWSL ∶ KHCO_3), have the most uniform spherical structure, the largest micropore occupancy(90.88%) and the highest oxygen content(22.17%). In the electrolyte of 6 mol/L KOH, a specific capacitance of 323 F/g(at the current density of 0.1 A/g) is obtained in the three-electrode system using the porous carbon sphares as electrode material. In addition, the assembled supercapacitor has the maximum energy density of 6.17 Wh/kg. After 20 000 GCD cycles at 2 A/g, the capacitance still retained 96% of initial, and the Coulombic efficiency is always 100%. This paper can provide theoretical support for the preparation of lignite based oxygen-enriched porous carbon materials.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 24125K]

  • Effect of metamorphic degree of bituminous coal on the pore and crystal structure of coal-based porous carbon by flash Joule heating

    WU Junchen;ZHANG Wenjun;ZHU Rongtao;LU Haozhi;SUN Yang;WANG Yajun;School of Chemical Engineering,China University of Mining and Technology;Key Laboratory of Coal Processing and Efficient Utilization of Ministry of Education,China University of Mining and Technology;

    Porous carbon was prepared by bituminous coal with different metamorphism degree and used K_2CO_3 as activators by flash Joule heating under different voltage. The effects of metamorphism degree of the bituminous coal and flash voltage on pore characteristics and crystal structure of porous carbon were investigated and characterized by a series of methods such as field emission scanning electron microscopy(FESEM), low temperature nitrogen adsorption and Raman spectra. Results show that the pressure effect and thermal expansion effect caused by the instantaneous high temperature through the Joule heating in the limited space are the driving forces for the pore formation and expansion. When the alkali-carbon ratio is 3∶1 and the flash voltage is 80 V, the pore structure of the porous carbon prepared from low metamorphic Shuozhou coal is the most developed with the specific surface area is 601.95 m~2/g and pore volume is 0.44 cm~2/g. The graphitization degree of porous carbon prepared from Changzhi coal with high metamorphic degree is the highest when the alkali-carbon ratio is 3∶1 and the flash voltage is 160 V.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 45901K]

  • Mechanism of coal thermochemical utilization based on DFT Methods: A review

    TANG Yumu;HUANG Rui;YU Yujie;LI Jianfeng;YAO Xianrui;HE Yu;School of Electrical Engineering,Guizhou University;

    Coal plays a leading role in current China′s primary energy consumption. Clean and efficient conversion of coal is an important part of building a clean, low-carbon, safe and efficient energy system in China. The critical information of electronic structure and geometric configuration from transition states which is difficult to be measured by experimental methods can be investigated by quantum chemistry method. The molecular release, migration and transformation process of coal thermochemical conversion are revealed from the micro level to provide theoretical guidance for the clean utilization of coal. The characteristics and functions of density functional theory(DFT)-based methods in the study of coal structure and reactivity were investigated and the application of thermochemical conversion mechanism in coal combustion pollutant removal, gasification, pyrolysis and liquefaction was summarized. The removal mechanism of NO_x and heavy metal pollutants in coal combustion, the promotion mechanism of coal char gasification reaction, the removal mechanism of oxygen-containing functional groups in coal pyrolysis and the hydrogen transfer mechanism in coal liquefaction were discussed. DFT methods can effectively reveal the properties of a certain aspect of coal and the characteristics shown in the reaction, but there is still a lack of comprehensive understanding of the molecular structure of coal. With the further improvement of relevant theoretical understanding, DFT methods will provide guidance for more clean utilization and conversion technology of coal through its advantages in micro-mechanism research.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 12035K]

  • Composition and ash melting point prediction of coal ash and biomass ash

    HUANG Kuilin;HAN Kuihua;QI Jianhui;School of Energy and Power Engineering,Shandong University;Shandong Engineering Laboratory for High-efficiency Energy Conservation and Energy Storage Technology & Equipment,Shandong University;

    Slagging in the furnace is one of the key factors affecting the reliable operation of thermal power units and gasification process. The safety and economy of the operation of thermal power units and gasifiers can be improved by accurate and timely measurement of ash melting temperature. However, there are many uncertain factors in the process of ash melting temperature measurement. The establishment of ash melting temperature prediction method cannot only verify the reliability of test data, but also replace the complicated test to a certain extent. The composition, classification methods, similarities and differences of coal ash and biomass ash were discussed, and the effects of different oxides on ash fusibility were summarized. Three main methods for predicting the melting temperature of coal and biomass ash, including empirical formulas, machine learning models, and multivariate phase diagrams, were described, and the advantages, disadvantages, and applicability of each method were analyzed. It is considered that the empirical formula is more suitable for the coal ash data set with single variety and small quantity, but it is not suitable for the prediction of biomass ash melting point. The machine learning model has good prediction effect on coal ash and biomass ash, but it is more difficult to model, which requires more training sample data. The prediction of ash melting temperature based on phase diagram is limited by the ash fusibility test method, and the prediction effect is not better than the empirical formula and machine learning model, but it has good prediction accuracy for four typical coal types, and the biomass ash has more special samples than coal ash. Further research is needed to determine whether it can be used for the prediction of biomass ash melting temperature. In the future, it is possible to consider building K nearest neighbor regression, random forest and other more outstanding models to solve regression problems and expand biomass database samples to improve the accuracy and generalization ability of the prediction model.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 11945K]

  • Preparation and catalytic cracking characteristics of coal tar cracking catalyst

    MENG Dechang;ZHAO Yuan;ZHANG Yaqing;JIAO Tiantian;GU Xiaohui;WANG Guangyao;LIANG Peng;Beijing Research Institute of Coal Chemistry,China Coal Research Institute Co.,Ltd.;State Key Laboratory of Coal Mining and Clean Utilization;School of Chemical and Biological Engineering,Shandong University of Science;

    The coal fast pyrolysis/circulating fluidized bed combustion/catalytic reactor coupled fractionation conversion process is easy to operate and maintain, with significant economic benefits, which is one of the effective ways to achieve clean and efficient utilization of coal resources. However, due to the poor tar quality and high pollution element content produced by the rapid coal pyrolysis process, the catalyst is frequently deactivated and regenerated. Therefore, a cheap and efficient non regenerative catalyst has been prepared in this paper. The effects of calcination temperature and modification method of catalyst on the catalytic cracking characteristics of coal tar were investigated in a fixed bed catalytic reactor with low-temperature coal tar as raw material and natural dolomite as research object. The 1% Ni/2%Fe dolomite catalyst was prepared under the optimum preparation conditions, and the effect of reaction temperature on the catalytic cracking of coal tar was investigated. The results show that with the increase of calcination temperature, the main components of dolomite, such as CaCO_3 and MgCO_3 is promoted to convert into CaO and MgO active substances, and the activity of natural dolomite catalyst gradually increases and tends to be stable, with the optimal calcination temperature of 750 ℃. The cracking of tar is not promoted by introducing Fe alone, but the catalytic activity of natural dolomite catalyst is significantly improved by introducing Ni and Fe at the same time. The best modification method is 1% Ni/2% Fe dolomite. The introduction of Fe as a promoter protects the sulfur poisoning deactivation of the active component Ni, while the introduction of Ni and Fe alleviates the sintering phenomenon of the catalyst. Fe can be used as an auxiliary agent to slow down the generation of carbon deposits in the catalytic process. The dolomite catalyst modified by Ni promotes the cracking of aliphatic compounds and sulfur-containing compounds. Indene and naphthalene compounds do not undergo cracking reactions, but products such as hydroindene and hydronaphthalene appear.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 28367K]

  • Gas generation characteristics of Shenmu bituminous coal in fluidized preheating

    ZHANG Zhen;ZHU Jianguo;SHI Yongshuai;WANG Tingting;School of Energy,Power and Mechanical Engineering,North China Electric Power University;Institute of Engineering Thermophysics,Chinese Academy of Sciences;University of Chinese Academy of Sciences;

    The preheating combustion is a novel effective and clean combustion technology with the technical advantages of wide fuel adaptability, high load adjustment and low pollutant emission. The preheating coal gas generated after the pulverized coal fluidization preheating can not only reflect the modification degree of the pulverized coal in a preheating process, but also play an important role in subsequent combustion efficiency and NO_x emission as well. Therefore, the preheating coal gas generated after the pulverized coal fluidization preheating is a key for controlling fuel conversion and low NO_x emission. Based on the pulverized coal fluidized preheating conversion process, the effects of preheating temperature, air equivalence ratio of CFB, and pulverized coal particle size on the preheated gas generation characteristics were investigated in this paper on a kW-stage pulverized coal preheating combustion experimental platform with controllable temperature. The results show that the pyrolysis and gasification reaction are enhanced with the increase of preheating temperature in the range of 850-950 ℃. The volume fraction of CO_2 in the gas decreases, the volume fraction of CO increases, the volume fraction of H_2 increases firstly and then remains unchanged, while the volume fraction of CH_4 increases firstly and then decreases. The gas quality is improved and the heat value increases from 2.86 MJ/m~3 to 3.61 MJ/m~3. When the air equivalent ratio of CFB increases from 0.3 to 0.5, the oxidation reaction is enhanced, the volume fraction of CO_2 in the gas increases, the volume fractions of CO, H_2 and CH_4 decreases, and the heat value of gas decreases from 3.44 MJ/m~3 to 2.04 MJ/m~3. With the increase of pulverized coal particle size, the residence time of pulverized coal in the riser is prolonged and the gasification reaction is enhanced. The volume fraction of CO_2 in the gas decreases, the volume fraction of CO and H_2 increases, the volume fraction of CH_4 increases first and then decreases, and the heat value of gas increases from 2.30 MJ/m~3 to 3.63 MJ/m~3.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 8731K]

  • Optimization of preparation of cellulose acetate/coal-based hierarchical porous carbon based on Design-expert

    CUI Kai;LI Tongda;WANG Fuquan;LUO Huafeng;School of Coal Engineering,Shanxi Datong University;

    The current utilization of coal-bed methane is direct combustion, which will generate a large amount of greenhouse gas(CO_2) emissions, and will also result in the use of scarce resources with low added value. In order to realize the high value-added utilization of coal-bed methane, it was proposed to prepare a cellulose acetate/coal-based graded porous carbon material by coal in-situ added cellulose acetate and KOH activation, and it was applied to the direct cracking of coal-bed methane to produce hydrogen. It not only can produce high-purity hydrogen, but also a certain amount of nano-carbon materials can be obtained. In view of the influence of temperature, alkali-to-carbon ratio, solvent amount and other carbon source addition on the preparation process and conversion rate in the preparation process of cellulose acetate/coal-based graded porous carbon, it was planned to use the Design-expert software to optimize the design of the experimental program. The relationship between each influencing factor and the conversion rate was analyzed by the response surface method and some experimental data, the corresponding fitting regression equation was established, and the theoretical optimal solution was obtained. Through comparing and analyzing the experimental value, the reliability of Design-expert software under multi-factor and multi-level conditions was verified, and the mechanism of carbon material catalytic cracking coal-bed methane under optimal conditions also was clarified. The results show that temperature and alkali-to-carbon ratio are the most influential factors in the preparation process of cellulose acetate/coal-based hierarchical porous carbon. The fitting regression equation between the relevant factors and the conversion rate is established and the theoretical optimal solution is obtained. The theoretical results are compared with the experimental results, the maximum error between the results is 3.05%, indicating that the Design-expert software is accurate and reliable in the optimization of the preparation process. The cellulose acetate/coal-based hierarchical porous carbon catalytic cracking coal-bed methane has a higher conversion rate and stability than the original coal material. After the reaction, the former produces a large number of carbon balls on the surface, while the latter produces a small amount of carbon fibers and a large number of carbon balls on the surface.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 13210K]

  • Emission characteristics test of SO_2,NO_x and dust from a 350 MW super-critical circulating fluidized bed boiler

    YUAN Zemin;HUANG Zhong;WU Guangjian;YANG Yunkai;YANG Hairui;ZHAO Guanjia;YUE Guangxi;MA Suxia;Key Laboratory of Clean and Efficient Combustion and Utilization in the Circulating Fluidized Bed,Taiyuan University of Technology;Department of Energy and Power Engineering,Tsinghua University;Jinneng Datuhe Power Plant Co.,Ltd.;

    To master the pollutant emission characteristics of a 350 MW supercritical CFB boiler under mixed combustion of multi-element low-calorific value coal including coal slime and coal gangue, taking a 350 MW supercritical CFB boiler of a power plant as the research object, and based on the measured data of on-site operation, the formation and emission characteristics of SO_2, NO_x and dust in flue gas were studied against the boiler load rate between 30% and 99%. Additionally, the key operated parameters including boiler operating load, average bed temperature, excess air coefficient and fluidizing air rate on its generation and emission level were investigated. The test results reveal that the flue gas pollutant emissions of the CFB unit can meet the emission standards within the load range of 30%-99% at total discharge outlet. The emission concentration of SO_2, NO_x basically decreases first and then increases rapidly with the decrease of boiler load. The concentration of dust emission decreases with the decrease of boiler load, and the dust emission concentration decreases with the reduction of boiler load. Among the key operating parameters studied, the boiler bed temperature plays a leading role in the emission level of SO_2, NO_x. The emission concentration of SO_2 and NO_x is higher with the lower average bed temperature and the larger excess air coefficient, and the emission concentration is basically positively correlated with the excess air coefficient and fluidization air rate. Considering comprehensively, it is recommended that the average bed temperature of the boiler should be properly controlled above 800 ℃, and the excess air coefficient should be stabilized less than 1.3. The way of flue gas recirculation can be used to reduce the oxygen concentration of the flue gas under low load on the basis of the maintaining the normal fluidization of the material.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 22406K]

  • Effect of burnout air rate and wall air on high temperature corrosion of water wall of 350 MW tangentially fired boiler

    FAN Jingyang;WANG Meng;PANG Long;PENG Zhimin;HU Yaohui;Neimenggu Kangbashi Thermal Power Co.,Ltd.;Department of Energy and Power Engineering,Tsinghua University;Department of Power Engineering,North China Electric Power University;

    Aiming at the high temperature corrosion problem of the water wall of a 350 MW low nitrogen boiler in a power plant, the simulation study was carried out to adjust the air distribution and increasing near-wall air. The relationship between the concentration of reducing gases CO, H_2S and NO_(x )in the furnace was simulated when the burn-out air rate was 38%, 33% and 27% respectively, and the effect of increasing the wall air on the concentration of reducing gases near the water wall was simulated. The results show that the burn-out air rate is reduced from 38% to 33%, which can reduce the concentration of reducing gases CO and H_2S in the furnace by 20% without significantly increasing the amount of NO_x, and slow down the high-temperature corrosion of the water wall. Reducing the burn-out air rate from 38% to 27% can increase the oxygen concentration in the main combustion zone, reduce the production of CO and H_2S, and slow down the high-temperature corrosion of the water wall, but the NO_x concentration will increase significantly. The high-temperature corrosion area in the furnace is mainly located between the UAP nozzle of the compact burnout air and the SOFA3 nozzle of the intermediate burnout air. The near-wall air can be added on both sides of the UAP nozzle of the compact burnout air. The simulation results show that the concentration of CO and H_2S near the water wall can be reduced by increasing the near-wall wind with the same rotation direction as the main flow, and there is the small effect on the flow field. Due to the high concentration of CO near the water wall, the flow of near-wall air on both sides is larger, which has better effect on reducing CO near the water wall. The coverage area of near-wall air on both sides is larger for high-temperature corrosion area, while the concentration of H_2S near the water wall is lower. There is no obvious difference between the single-side near-wall air and the double-side near-wall air in reducing the H_2S of the water wall, but the double-side near-wall air will disturb the distribution of the flow field, which is not conducive to pulverized coal combustion.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 26206K]

  • Dynamic characteristic of heat transfer process during sensible heat recovery of raw coke oven gas in ascension pipe

    PENG Wenping;JIN Zhiping;LU Gailin;BAI Tao;ZHENG Lixing;GUO Congxiu;School of Electric Power,Civil Engineering and Architecture,Shanxi University;

    Carbon deposition of coal tar is the main factor that restricts the long term efficient and safe operation of the ascension-pipe heat exchanger for recovering sensible heat of raw coke oven gas(COG). It is an effective measure to prevent carbon deposition of coal tar by controlling temperatures of raw COG and inner wall of ascension pipe. Based on local non-thermal equilibrium idea of porous media, a one-dimensional unsteady heat transfer model was established for the ascension-pipe heat exchanger with embedded spiral coils and porous fillers for sensible heat recovery of raw gas. Based on the instantaneous data of raw gas flow and temperature during the coking cycle, the dynamic characteristics of temperatures of raw COG, wall of ascension pipe, packing layer and molten salt were obtained. The effects of the heat capacity of filler layer, effective thermal conductivity of filler layer, and molten salt flow rate on its dynamic changes were analyzed. Moreover, a method was proposed to effectively control temperatures of raw COG and wall of ascension pipe. The results show that the coal tar precipitation mainly occur in the late coking period when raw COG output will decrease quickly. The thermal conductivity of packing layer is an important parameter to be considered in the design of the ascension-pipe heat exchanger. Increasing the conductivity of packing layer can improve the heat recovery efficiency, but also make the temperature drops of raw COG and wall of ascension pipe increased. The thermal conductivity of the packing layer should be increased as far as possible under the premise of ensuring that the tar vapor does not condense. In the later stage of coking, the temperature control of the rising pipe wall can be realized by cutting off the molten salt to get heat, and reasonably designing the thermal conductivity of packing layer, the heat capacity of packing layer and the inlet temperature of molten salt, so as to avoid the coal tar precipitation.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 34854K]

  • Regulation mechanism of polycarboxylate acid superplasticizer on hydration process of fly ash-based slurry

    CHU Ruizhi;YAN Yaoqi;YANG Wei;LUO Weidong;REN Wanxing;MENG Xianliang;Institute of Chemical Technology,China University of Mining and Technology;Guizhou Panjiang Coal and Electricity Group Technology Research Institute Co.,Ltd.;School of Safety and Engineering,China University of Mining and Technology;

    The fluidity of fly ash-based shotcrete material plays a very important role in practical engineering applications. In order to explore the regulation mechanism of water reducing agent on the fluidity of fly ash-based slurry, the effects of different water reducing agent dosage on slurry flow performance were compared through the characteristics of reducing water rate, fluidity, setting time, slurry viscosity and shear stress, and the best water reducing agent and dosage were selected. The change law of hydration process and time of flyash-based slurry by polycarboxylate acid superplasticizer(PCE)was emphatically explored by using hydration heat analyzer, X-ray diffraction and scanning electron microscope and the hydration mechanism of shotcrete materials with PCE was proposed. The results show that PCE has the most obvious improvement on flow performance of fly ash base slurry. When the saturated content is 0.6%, the water reduction rate can reach 29.3%, the fluidity extends from 113 mm to 351 mm, the initial setting time is extended from 32 min to 149 min, and the final setting time is extended from 42 min to 182 min, with a significant delayed setting phenomenon. In the early hydration process, The adsorption of PCE can inhibit the dissolution of C_3A, hinder the growth of ettringite(AFt) and change its crystal form. At the same time, the complexation of PCE can combine with Ca~(2+ ) to form complex, affecting the formation of Ca(OH)_2, delaying the enrichment of Ca~(2+) and prolonging the induction period of cement hydration. The hydration of C_3S is also inhibited, which reduce the number of C-S-H nucleation and the second hydration exothermic peak. In the middle and late stages of hydration, the inhibition effect of PCE fails and the mechanical strength of the material increases gradually. PCE can only delay the early hydration process, but has no effect on the middle and late hydration process.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 31501K]

  • Present situation and prospect of research on mechanism of inhibiting coal spontaneous combustion by aerobic microorganisms

    YI Xin;ZHANG Shaohang;GE Long;BAI Zujing;DENG Jun;School of Safety Science and Engineering,Xi′an University of Science and Technology;Shaanxi Key Laboratory of Prevention and Control of Coal Fire;

    The research status of microbial desulfurization and degradation of coal was summarized. The treatment of coal with aerobic microorganisms can reduce the sulfur content(pyrite), destroy the active groups such as hydroxyl, carbonyl and carboxyl in coal, consume oxygen and produce carbon dioxide gas. The idea of using biotechnology to delay the coal oxidation process and blocking coal oxidation path so as to inhibit the spontaneous combustion of coal was put forward. This is based on the use of the characteristics of microorganisms to change the environmental state and microstructure of the coal surface to prevent and control spontaneous combustion of coal from the coal oxidation reaction itself. In view of the effect of aerobic microbial modification and domestication on the sulfur content and active groups of coal, the commonly used microorganisms for coal desulfurization and degradation(such asAcidthiobacillus ferrooxidans, Phanerochaete chrysosporium, etc.) were analyzed, and the growth characteristics and differences of microorganisms that could be used to inhibit coal spontaneous combustion were summarized. Finally, the idea that the spontaneous combustion of coal could be inhibited by the step-by-step synergy of various functional microorganisms was proposed, and a new prospect for the development of new green inhibitors of coal spontaneous combustion was made.

    2023 02 v.29;No.150 [Abstract][OnlineView][HTML全文][Download 7274K]